50 hz refresh rate in Mac OS X Yosemite

Hi,
I'm using openMSX in Mac OS X Yosemite in a Mac Mini and I cannot set a 50 hz refresh rate to emulate a PAL MSX.
To achieve that in Windows 7 what I do is to switch the Windows desktop refresh rate to 50 hz and afterwards I run openmsx.
Unfortunately this same procedure doesn't seems to work in Mac OS X, whenever I run openMSX it switches to 60hz regardless of the current desktop resolution.
Any ideas?

Are you running in full screen? Are you running with full-throttle (set throttle off)?
Does openMSX really say it's running at 60Hz? Which speed (percentage) does it say it's running? (For both: try toggle_info_panel in the console.)

Well, I didn't explained correctly.
When I say "whenever I run openMSX it switches to 60hz regardless of the current desktop resolution", I mean the PC refresh rate, not the MSX FPS. Ah, and this happens only in full screen mode.
About the emulated MSX refresh rate, according to toggle_info_panel, it says 50 FPS for CBIOS MSX2+ (Localization: EU/INT). And throttle is "true".

Let me put it differently: there is no code in openMSX that attempts to sync with vertical refresh. So, it's probably something SDL is doing. This is something we can't fix without modifying SDL. In the long run, we'll upgrade to SDL2 and later to another framework, which will hopefully fix this. But don't count on it soon.

What about to add to the 'set fullscreen' command the option fullscreen_windowed? This option would generate a borderless window and fully maximized, hiding the desktop. By implementing this option the desktop current refresh rate, either 60 or 50hz, would be kept.